Change account layout

[bmuddha]

Modify account layout in accounts database:

1. reuse slack space which is available in block allocation if possible,
   this avoids reallocation of accounts if the data field grows
   insignificantly.
2. track account owner change to avoid index checks in happy path

depends on #419
closes #443
closes #441

Greptile Summary

Major refactoring of AccountsDB storage and indexing system to optimize account data storage and improve performance through block space reuse and owner tracking.

• Consolidated multiple LMDB environments into a single environment and introduced new Table abstraction in magicblock-accounts-db/src/index/table.rs for better database operation encapsulation
• Modified account serialization in magicblock-accounts-db/src/lib.rs to reuse slack space in block allocations, reducing unnecessary reallocations for small data growth
• Added owner change tracking to optimize index checks by skipping them in the happy path when owner hasn't changed
• Improved LMDB iteration safety and efficiency in magicblock-accounts-db/src/index/iterator.rs by removing manual cursor management
• Changed program account iteration behavior to return empty iterators instead of NotFound errors for better API consistency

[greptile-apps]

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